I. Field of the Invention
The present invention relates generally to riding trowels used for finishing concrete surfaces. More particularly, the present invention relates to high powered, motorized riding trowels that are supported and steered by downwardly projecting, tiltable rotors. Known, representative self propelled riding trowels are classified in United States Patent Class 404, Subclass 112.
II. Description of the Prior Art
As will be recognized by those skilled in the art, motorized trowels can effectively finish large surface areas of wet concrete. Motorized riding trowels are particularly effective in this regard. Motorized "push trowels" and riding trowels often employ revolving rotors that directly contact the concrete surface. The rotors typically comprises a plurality of radially spaced apart finishing blades that revolve in frictional contact the with concrete surface. The rotors support the entire weight of the trowel. While a wide variety of manually pushed troweling machines or "power" trowels are currently used in the industry, self propelled riding trowels efficiently finish large areas of concrete more swiftly than motorized "push trowels."
During trowel finishing operations, the trowel must traverse the concrete surface several times as the concrete sets, and generally the more powerful the trowel, the faster the operation can be completed. In relatively recent years motor powered riding trowels have become popular. With riding trowels descended from Holz patents U.S. Pat. Nos. 4,046,484 and 3,936,212 steering and control is effectuated by the combination of rotor tilting and blade twisting. The rotors are driven by a self contained engine mounted on the frame that is linked to rotor gearboxes. A driver seated above the frame steers the trowel by tilting the axis of rotation of the rotors. The pitch of each trowel blade adjusts by pivoting about its longitudinal axis. A yoke controlled bearing assembly is often employed to vary the blade pitch.
Riding trowels typical of those present in the art are disclosed in two patents issued to Holz, U.S. Pat. Nos. 4,046,484 and 3,936,212. The latter patent depicts a three rotor trowel, while the former depicts an early twin rotor trowel. Both devices are powered by a single motor.
I have been involved with several prior motorized trowel inventions. U.S. Pat. No. 5,108,220 relates to a fast steering system for riding trowels. It discloses a state of the art steering system for riding trowels that enhances maneuverability and control. U.S. Pat. No. Des. 323,510 also discloses a riding trowel.
Kikuchi, U.S. Pat. No. 4,775,306, discloses a multiple engine trowel that does not use the rotors for propulsion or steering. This device is not the type of trowel pioneered by Holz listed above. A pair of drum-like crawlers are separately employed to support the trowel, and they are powered for locomotion. The blades define a wiping annulus upon the concrete surface that circumscribes the crawlers. An unfinished area within the wiping blade perimeter results, and energy is wasted as the frictional contact of the blades is merely dissipated as heat rather than providing propulsion or steering.
Most current riding trowels in the Holz species employ two sets of bladed rotors. The sweep areas of the rotor blades often overlap to avoid intermediate seams or surface blemishes. In other words, the propeller-like blades properly mesh to avoid unfinished boundary strips. With relatively larger diameter surface finishing pans, no overlap occurs. Typically such rotors must rotate at the same speed to prevent blade collision. Known current trowels use a single engine that ensures that the rotors are properly synchronized. However, a relatively slow finishing speed results from the low power output of single engine designs. Since concrete must be finished before setting, the finishing speed of the trowel is important.
At very large pour cites it is often difficult to finish all of the concrete surface area before the concrete significantly sets. Thus more powerful riding trowels are continually evolving. Typical single engine machines are being equipped with more and more powerful engines.
However, bigger engines can result in problems. A very large engine makes structural demands on the frame, the rotors and the drive train. Obviously, because the rotors are in direct wiping contact with the concrete surface being treated, a typical twin rotor trowel is already under considerable stress. One problem is caused by the transmission of vibrations from the blades to the dynamic components and drive train of the trowel. Vibrations can easily damage the engines, which are expensive to repair. Since contra-rotation of the rotors is typical, preservation of mechanical symmetry in the critical motor-to-rotor gearbox system with a single engine is a challenge yet to be solved.
On multiple rotor trowels, it is desirable to substantially isolate the individual rotors and their gearboxes from the other rotors and gearboxes. Therefore, when one rotor or gearbox breaks, the other rotors and gearboxes are hopefully undamaged. However, single engine designs are deficient in this respect. For example, damaging stresses resulting from impact of one rotor with an "immovable object" are often transmitted to the other rotor drive train with typical older designs.
Obviously trowel breakdown during critical concrete setting necessitates immediate repairs at the job sight. Since one of the most routinely troublesome components is the gearbox, an interchangeable gearbox that would fit any of the rotors on a multiple rotor trowel would diminish down time. An interchangeable gearbox would decrease the quantity of spares that must be kept in stock for repairs.
To minimize problems with powerful self propelled riding trowels I have proposed a twin engine design in my co-pending application referenced above. In this application I have improved the engine mounting scheme, the power train, and the overall design, after extensive product testing, so as to maximize reliability.